Careful handling is required when shipping or storing semiconductor materials and devices such as wafers as they are very fragile and susceptible to fracture and contamination by the surrounding atmosphere. FIGS. 7 and 8 illustrate one of typical prior art packaging containers heretofore widely used for shipping and storing semiconductor wafers. As shown in FIGS. 7 and 8, the packaging container comprises a lower circular case member 2 having a conncave bottom wall 2a which is adapted to support a wafer A thereon, a dish-shaped retainer 4 having a plurality of radial arms 4a extending radially outwardly therefrom, and a mating upper case member 6 adapted to fit over the lower case member. When mated with the lower case member, the upper case member urges the retainer 4 to press the radial arms 4a against the peripheral margin of the wafer A to thereby hold the wafer between the case members.
While such conventional container is very effective to package circular wafers, it has been found unsuitable to package rectangular wafers, since a rectangular wafer contacts only on its four corners with the concave bottom wall of the lower case member 2, so that stresses tend to be concentrated on the four corners to possibly break the wafer at the corners. In addition, pressing forces exerted on the wafer by the retainer 4 tend to produce internal strains within the wafer material, resulting in undesirably degrading the wafer quality.